Successful treatment of infective endocarditis often requires cardiac vlave replacement during the active infection. This is especially the case with aortic valve infection, and with infection of valve prostheses in either the aortic or mitral position. Valve excision with or without replacement, however, is also sometimes required for tricuspid valve infection. This discussion will focus on the morphologic aspects of active infective endocarditis involving both right and left-sided native cardiac valves. It will also examine certain morphologic aspects of mechanical and bioprosthetic valve substitutes. The information is derived from necropsy examination by the authors of 192 patients with active infective valvular endocarditis. Patients with infective endocarditis complicating congenital heart disease with a shunt (6 patients), and those with infective endocarditis following valvulotomy (4 patients) are omitted from this analysis.